Does anyone have a reliable source for receiver CAD part files for inventor? I am looking for something I can download and not be worried about viruses/spam. I have really wanted to machine in some artwork to a lower, and now I am thinking about cncing the whole thing.

Originally Posted By racerpk11:3dcontentcentral.com has just about everything I believe.

A quick search for "ar-15" there provided a wealth of data. Many more parts than just lowers. I didn't look beyond page 1, but judging by what was there I'd guess that site has schematics for almost everything short of a barrel, well at least the barrel rifling (that requires special tools beyond a CNC).

"A kid is dead and guys are talking about fucking her mom who let her die of neglect.

Thats where I found the base for a custom upper/lower job I am doing in my spare time. Like you said they have about everything you need if you wanted to build up a full assembly and show a cut away of the internals.